This invention relates to an interface apparatus and method and an image output apparatus having the interface apparatus and, more particularly to an interface apparatus for transmitting/receiving information with an external apparatus via a communication line, a method for negotiating for transmitting/receiving information between apparatuses, and an image output apparatus having the interface apparatus.
Generally, a printer and an information processing device are connected via a fixed type communication interface. In each device, an open-collector type interface circuit or totem-pole type interface circuit is fixedly provided, and it is impossible to select an interface circuit in accordance with the specification of communication destination device.
However, in a case where a device has only an open-collector type interface circuit, even if another device as a communication destination uses a totem-pole type interface, high-speed communication cannot be performed. In an open-collector type interface circuit, a transitional period where a signal level changes from a high level to a low level, and a transitional period where the signal level changes from the low level to a high level are greatly different. Especially, the transition of signal level from the low level to the high level is made very slowly.
In a case where the device has only a totem-pole type interface circuit, if the power of the communication destination device is turned off and the communication line is in short-circuit or in low-impedance status, overcurrent occurs, which consumes a large amount of electricity and may cause the interface circuit to generate heat.
There is a tendency of signal voltage swing to be complicated, since small signal voltage swing is used to increase communication speed or to save electricity. A device corresponding to only one signal voltage swing cannot handle communication with devices of various specifications. In many cases, the input characteristics of signals and the output characteristics of signals do not coincide with each other.
Further, even though the device can communicate with a high-performance device, if the device cannot communicate with existing devices, it cannot be efficiently utilized. For example, it is inconvenient that every time a new device is introduced, all the devices to be connected to the new device must be changed.
The present invention has been made in consideration of the above problems, and has its object to provide an electronic device which can be appropriately connected to external devices having various specifications.
According to the present invention, the foregoing object is attained by providing an interface apparatus for transmitting and receiving information with an external device via a communication path, comprising: acquisition means for acquiring selection information supplied from the external device via the communication path; and drive means for selecting one of a plurality of drive methods based on the selection information acquired by the acquisition means and driving the communication path.
Preferably, in the interface apparatus, the plurality of drive methods includes a first drive method for driving the communication path in an open-collector drive and a second drive method for driving the communication path in a totem-pole drive.
Preferably, in the interface apparatus, the plurality of drive methods includes a plurality of drive methods for driving the communication path with signal voltage swings different from each other.
Preferably, in the interface apparatus, the communication path is a communication path for bidirectional parallel interface.
Preferably, in the interface apparatus, the selection information is information for selecting a communication mode of communication between the external device.
Further, according to another aspect of the present invention, the foregoing object is attained by providing an interface apparatus for transmitting and receiving information with an external device via a communication path, comprising: acquisition means for acquiring selection information supplied from the external device via the communication path; and input means for setting a threshold value as a reference value for inputting a signal on the communication path, based on the selection information acquired by the acquisition means, and inputting information supplied from the external device via the communication path, with the threshold value as the reference value.
Preferably, the interface apparatus further comprises signal voltage-swing selection means for selecting a signal voltage swing upon driving the communication path based on the selection information acquired by the acquisition means, and the communication path is driven with the signal voltage swing selected by the voltage-swing selection means.
Preferably, in the interface apparatus, the input means includes: a plurality of input devices, having input terminals connected to the communication path, and employing threshold values different from each other; and a selection device for selectively inputting a signal on any of output terminals of the input devices, based on the selection information.
Preferably, in the interface apparatus, the selection information is information for selecting a communication mode of communication between the external device.
Further, according to another aspect of the present invention, the foregoing object is attained by providing an interface apparatus for transmitting and receiving information with an external device via a communication path, comprising: acquisition means for acquiring selection information supplied from the external device via the communication path; drive means for selecting any of a plurality of drive methods based on the selection information acquired by the acquisition means, and driving the communication path; and input means for setting a threshold value as a reference value for inputting a signal on the communication path, based on the selection information acquired by the acquisition means, and inputting information supplied from the external device via the communication path, with the threshold value as the reference value.
Preferably, in the interface apparatus, the plurality of drive methods includes a first drive method for driving the communication path in an open-collector drive and a second drive method for driving the communication path in a totem-pole drive.
Preferably, in the interface apparatus, the plurality of drive methods includes a plurality of drive methods for driving the communication path with signal voltage swings different from each other.
Preferably, in the interface apparatus, the input means includes: a plurality of input devices, having input terminals connected to the communication path, and employing threshold values different from each other; and a selection device for selectively inputting a signal on any of output terminals of the input devices, based on the selection information.
Preferably, in the interface apparatus, wherein the communication path is a communication path for bidirectional parallel interface.
Preferably, in the interface apparatus, the selection information is information for selecting a communication mode of communication between the external device.
Further, according to another aspect of the present invention, the foregoing object is attained by providing an interface apparatus for connecting a plurality of devices via a communication path, comprising: selection-information supply means for supplying selection information from one device to another device via the communication path; and selection means for selecting one of a plurality of drive methods for driving the communication path from the side of the other device, based on the selection information supplied by the selection-information supply means, wherein transmission and reception of information between the devices is performed by driving the communication path in the drive method selected by the selection means.
Preferably, the interface apparatus further comprises setting means for setting a drive method for driving the communication path in correspondence with the selection information, on the side of the one device.
Preferably, in the interface apparatus, the plurality of drive methods, selectable by the selection means, includes a first drive method for driving the communication path in an open-collector drive and a second drive method for driving the communication path in a totem-pole drive.
Preferably, in the interface apparatus, the plurality of drive methods includes a plurality of drive methods for driving the communication path with signal voltage swings different from each other.
Preferably, in the interface apparatus, the communication path is a communication path for bidirectional parallel interface.
Preferably, in the interface apparatus, the selection information is information for selecting a communication mode of communication between the external device.
Further, according to another aspect of the present invention, the foregoing object is attained by providing an interface apparatus for connecting a plurality of devices via a communication path, comprising: selection-information supply means for supplying selection information from one device to another device via the communication path; and selection means for selecting one of a plurality of threshold values as a reference value for inputting a signal on the communication path, based on the selection information supplied by the selection-information supply means, on the side of the other device.
Preferably, the interface apparatus further comprises setting means for setting one of the plurality of threshold values as the reference value for inputting the signal on the communication path in correspondence with the selection information, on the side of the one device.
Preferably, the interface apparatus further comprises means for driving the communication path with a signal voltage swing corresponding to the selection information, from the side of the one device; and means for driving the communication path with a signal voltage swing corresponding to the selection information, from the side of the other device.
Further, according to another aspect of the present invention, the foregoing object is attained by providing an image output apparatus, comprising: an interface apparatus having the above construction; and image formation means for forming an image based on information inputted by the interface apparatus.
Preferably, in the image output apparatus, the image formation means forms the image by an electrophotographic method.
Preferably, in the image output apparatus, the image formation means forms the image in an ink-jet method.
Further, according to another aspect of the present invention, the foregoing object is attained by providing a method of negotiating for transmitting and receiving information with an external device via a communication path, comprising: an acquisition step of acquiring selection information supplied from the external device via the communication path; and a determination step of determining one of a plurality of drive methods as a drive method for driving the communication path, based on the selection information acquired at the acquisition step.
Further, according to another aspect of the present invention, the foregoing object is attained by providing a method of negotiating for transmitting and receiving information with an external device via a communication path, comprising: an acquisition step of acquiring selection information supplied from the external device via the communication path; and a determination step of determining a threshold value as a reference value for inputting a signal on the communication path, based on the selection information acquired at the acquisition step.
Further, according to another aspect of the present invention, the foregoing object is attained by providing a method of negotiating for transmitting and receiving information with an external device via a communication path, comprising: an acquisition step of acquiring selection information supplied from the external device via the communication path; a drive-method determination step of determining one of a plurality of drive methods as a drive method for driving the communication path; and a threshold-value determination step of determining a threshold value as a reference value for inputting a signal on the communication path, based on the selection information acquired at the acquisition step.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same name or similar parts throughout the figures thereof.